Patent Document 1 (Japanese Patent Application Publication No. 2010-056355 A) discloses a technology for transfer-molding a substrate on which electronic components have been mounted with sealing resin. A semiconductor device disclosed in Patent Document 1 includes a plurality of substrates, at least one of which has electronic components mounted on both surfaces thereof. The plurality of substrates is disposed in a stacked manner with a space therebetween. Further, this semiconductor device includes a supporting structure configured to keep the space between the substrates constant.